1.1 [count noun] Philosophy A property or group of properties of something without which it would not exist or be what it is:Locke’s scepticism about our ability to penetrate to the real essences of things

Whereas the immediate explanation of the actuality of Aristotle's substances lay in what they were essentially, that was not the case with Avicenna's essences, for their status was that of the merely possible.

That is, items in all the categories are definable, so items in all the categories have essences - just as there is an essence of man, there is also an essence of white and an essence of musical.

Origen

Essence comes via Old French from Latin essentia, from esse ‘to be’. An early meaning was ‘being, existence’. In alchemy it was used in the phrase fifth essence or quintessence. Alchemists believed this substance to be latent in all bodies and thus to be extractable by distillation: this probably led to essence's use for ‘an extract obtained from a plant with therapeutic qualities’, reinforced by the sense ‘indispensable quality or constituent’.